Inkers usually, alternately, have rollers with hard, or unyielding, and a soft, or yielding surface. The rollers with the hard, unyielding surface may be axially oscillating, and are the distribution and milling rollers. A fountain roller, operating in an ink trough, and having a metered film of ink applied thereto by a doctor blade, is driven at a speed which is slow with respect to machine speed, which, usually, determines the circumferential speed of a plate cylinder of the printing machine. The first milling or distribution roller with which the lifter will come in contact is, usually, also positively driven at the machine speed, for example by gearing, which also drives all other rollers having hard surfaces. The gearing is, customarily, also geared to the plate cylinder.
The lifter oscillates between the fountain roller and the first milling or distribution roller, to apply the required quantity of ink from the fountain roller to the first milling or distribution roller for subsequent distribution, and further splitting of the ink film and eventual application to the printing plate of a plate cylinder. The soft surface roller which is in contact with the first milling or distribution roller usually is not driven, but carried along by circumferential or surface friction, in engagement with the first, and a subsequent, or second milling or distribution roller which, likewise, is driven. During the contact of the lifter roller with the first milling or distribution roller, the lifter roller is accelerated; upon contact with the fountain roller, which operates at a much slower speed, the lifter roller is decelerated.
It has been found that, with increasing operating speed of printing machines, or, with increasing diameter of the cylinders--which, likewise, may correspond to an increased circumferential speed of the printing cylinders, and, additionally, with increase in the width of the rollers to be able to print on wider webs or sheets, inking can become defective and the printed copy has defective points or zones, thus detracting from overall print quality. Various measures have been tried to reduce non-uniformities in printing. Pressure placed on bearer rings, and, if provided, selectively also on the bearer rings of blanket cylinders, if the printing machine is an offset printing machine, have been tried; further, adjustment in lateral register has been changed; it was believed that the reason for poor copy coming off the printing machine was due to maladjustment of bearer ring pressure, lateral register, and the like.